The present invention relates to a torque-limiting return stop device, which comprises a freewheel with an internal ring, an external ring concentric in reference thereto, and several retaining elements arranged in an annular gap between the internal and the external ring, which permit a relative rotation between the internal and the external ring in one direction, and block it in the other direction in a form-fitting or friction-fitting fashion, with the return stop device additionally comprising a flange at the attachment side and a housing part, between which the external ring can be interlocked, as well as a clamping device acting in the axial direction, which applies a contact pressure, preferably an adjustable one, by which the external ring is pressed with its face against at least one friction area between the flange and the housing part in order to generate a friction-fitting connection between the flange and the external ring, and with the return stop device furthermore comprising at least one releasing device, which is embodied to at least partially overcome the contact pressure of the clamping device in order to reduce or release the friction-fitting connection.
A generic return stop device is described for example in the product specification sheets in the catalog 84, issue 2013/2014, pages 72 to 75 of the applicant. This describes the attachment of freewheels of the series FXRV and FXRT, which description is included in its entirety herein by reference as if fully set forth.
Conveyer systems of most various types are very important for the infrastructure everywhere. Conveyer systems with continuous conveyance represent a considerable portion of these conveyer systems. They can reach a length of conveyance extending over many kilometers with mass flows totaling several ten thousand tons per hour and conveyance heights of several hundred meters.
When continuous conveyer systems are used for conveying items to different elevations, particularly in case of upwards conveying diagonal conveyer systems, safety measures must be implemented to prevent that, driven by the weight of the goods being conveyed, the continuous conveyer system tries to run backwards when an interruption occurs in the drive train. For this purpose return stop devices are used. They operate fully automatically and immediately prevent the downwards motion of the conveyer belt without here any relevant reverse motion developing and only minor kinetic energy being generated in the system.
When in continuous conveyer systems with several drive units multiple drives are provided, each with a separate return stop device, in case of a malfunction of the drive the problem arises of an uneven distribution of the reverse torque upon the individual transmissions and return stop devices. When the system is idle, the entire reverse torque initially acts primarily only upon one return stop device, due to the different play and elasticity of the drives involved. The return stop devices are equipped with torque limiters in order to prevent impermissible torque peaks from leading to the destruction of individual transmissions and corresponding return stop devices, which can progress up to major damage of the entire conveyer system.
The torque limiter installed in a return stop device permits a brief reverse motion of the drive shaft that is connected to the return stop device, amounting to only a few angular degrees, when the predetermined slippage torque has been exceeded, until successively the other return stop devices engage. This achieves that the entire reverse torque of the conveyer system is rather evenly distributed over the individual return stop devices and transmissions. Additionally, the dynamic torque peaks of the blocking operation are reduced such that the transmissions are protected from damaging torque peaks. Accordingly, by using torque limiters in connection with multiple drive units, the transmissions used can be dimensioned smaller.
In order to allow a limited reverse motion of the conveyer system when malfunctions occur in the drive, jamming at the conveyer belt etc., the return stop devices may be equipped with controlled release devices. Such a release device may for example be embodied such that it at least partially overcomes a contact pressure, by which the friction-fitting connection is generated in the torque limiter, in order to this way allow a controlled slippage of the torque limiter even below the predetermined maximum torque, for example during maintenance tasks. In release devices of prior art this occurs via large release screws.
The attachment of return stop devices occurs usually at a reduction gear unit on a fast-running shaft in order to operate at a speed as high as possible and thus correspondingly with smaller torques. Such transmissions are today increasingly designed in a more compact fashion and yet they can transmit increasing forces, so that stronger return stop devices become necessary. Due to the fact that the external diameter of the return stop device is limited by the dimensions of the transmission housing and the shaft distances though, it must be designed in a more compact fashion as well. Since a limiting of the torque is achieved in the torque limiter by way of friction-fitting connections, and the slippage torque is adjusted by an appropriate adjustment of the pressure upon the area, here a higher maximum torque with simultaneously a more compact design can only be achieved by an increase of the contact pressure in the torque limiter. However, this leads on the one side to the necessity of a higher number of release screws to overcome the contact pressure. This is however disadvantageous, because the release must occur very quickly, when required, therefore the number of release devices should be as low as possible.